The invention relates to a device for building a layer body from a plurality of superimposed layers of free-flowing material, in particular particulate material, on a building platform in a build space, the layers being solidified and joined together in locally predetermined areas through the action of a binder, so that at least one molding is formed by the solidified and joined areas of the layers, including an elongated discharge container, which is movable back and forth over the build space in at least one discharge direction and which has at least one discharge opening from which the free-flowing material is dischargeable in individual superimposed layers during the movement of the discharge container, it being possible to supply the discharge container with free-flowing material from a filling device with at least one storage or filling container having at least one outflow opening by vertically covering the at least one outflow opening of the storage or filling container with an elongated feed opening of the discharge container, according to the definition of the species in Patent Claim 1.
A computer-controlled method for producing three-dimensional moldings is described in EP 0 431 924 B1. Free-flowing particulate material is applied in a thin layer to a build space which is surrounded by container walls and is disposed on a building platform, and subsequently a binder is selectively printed thereon, using a print head, according to computer data. The particle area onto which the binder is printed sticks together and solidifies under the influence of the binder and, if necessary, an additional hardener. The building platform is then lowered by a distance of one layer thickness into a build cylinder and provided with a new layer of particulate material, which is also printed as described above. These steps are repeated until the desired height of the molding is achieved. A three-dimensional object is thereby produced from the printed and solidified areas.
After it is completed, the molding produced from solidified particulate material is embedded in loose particulate material and is subsequently removed therefrom. This is done, for example, using an extractor. This leaves the desired molding, from which the remaining adhering particles are removed, for example by brushing.
Other powder-supported rapid prototyping processes work in an identical or similar manner, for example, selective laser sintering or electron beam melting, in which loose particulate material is also applied in layers and selectively solidified with the aid of a controlled physical radiation source. The aforementioned methods are summarized under the terms, “additive manufacturing,” “three-dimensional printing” or “3D printing.”
EP 1 872 928 A1 proposes to raise the discharge container and the print head relative to the building platform instead of lowering the building platform relative to the discharge container and print head as the layering process progresses for building larger three-dimensional moldings. For this purpose, the discharge container is designed as a dosing device which may undergo controlled activation and deactivation for the controlled output of a predetermined, preferably constant, linear volume flow of particulate material per length unit and per time unit, so that particulate material is not unnecessarily strewn around the molding to be built or is not “emptied” prematurely and thus does not lose its function while the layer is being deposited. However, such dosing-controlled and “intelligent” discharge containers have a relatively complex structure and are correspondingly expensive.
“Unintelligent” discharge containers of a simpler design, on the other hand, are unable to dose particulate material in a targeted manner or are not switchable. For example, they include a scraper moving in the discharge direction or a counter-rotating roller or an oscillating blade. These devices then distribute a quantity of material in front of the discharge container on the build space in the discharge direction. The amount of particulate material then has to be sufficiently measured before the discharge container travels over the build space.
In order for the process to progress as described, the discharge container must pass completely over the area to be coated or the build space. The length of the discharge container therefore corresponds to the length of the build space. “Length of the discharge container” is understood below to be the largest dimension or the longest extension of the discharge container.
Discharge containers are therefore usually designed as an elongated beam having a hopper-shaped cross section and having a slot on the underside as the discharge opening for discharging particulate material. The longitudinal extension of the discharge container is then perpendicular to its discharge direction. The storage or filling container then has the function of filling the discharge container with the free-flowing material up to a desired fill level evenly and without losses over its entire length.
A beam-shaped storage or filling container is described in the generic WO 2010/149133 A1, which is provided with a hopper-shaped cross section, viewed on a plane perpendicular to the longitudinal direction, and which has the same length as the discharge container to be filled.
To be filled, the discharge container then passes under the storage or filling container at one end of the build space. The storage or filling container is emptied into the discharge container by means of a sliding closure of the outflow opening, which is provided with a grate, on its underside. Since the sliding closure extends over the entire length of the storage or filling container, it has a long and narrow structural design. This promotes the tendency of the sliding closure to become jammed. In addition, a relatively large amount of energy must be expended to move the sliding closure.
In WO 2005/097476 A1, the discharge container is filled with the aid of nozzles, which are moved along the discharge container. The nozzles are connected to a storage tank by flexible hoses. The powder is transported from the tank to the nozzle with the aid of a pump. To be able to move the hoses without kinking, the building device must have a certain height, which, however, causes the building device to have a large structural design. Transporting the powder in hoses is furthermore considered to be negative, due to high internal friction and siphon effects. If ribbed hoses are used to improve the mobility of the hoses, a high degree of contamination must be expected. If damp powder material is used, which tends to stick, cleaning the hoses becomes very complicated. During the movement of the hoses, pumping effects furthermore occur, which may compress the powder material, which, in turn, increases friction and impairs transport. Undesirable clumping may also occur. In addition, the delivery route from the storage tank to the nozzles is relatively long, and the powder comes into contact with the inner walls of the hoses, whereby the physical properties of the powder may change. Not least, to avoid overfilling the discharge container, either the pump must regulate the powder flow or the ratio between the powder flow and the speed at which the nozzles move must be controlled. However, both options require a great deal of control complexity, including additional sensors.
The object of the invention is therefore to refine a device of the type mentioned at the outset in such a way that a reliable filling of the discharge container is facilitated while maintaining a simple and cost-effective design.